For many capacitive MEMS devices, the use of electrodes above and below the device structure is either required for the basic operation of the device or greatly enhances the performance of the device. One or more of the electrodes are typically formed by deposition of a conductive film, electrical isolation of a conductive layer, or by simply adding a spacer layer between two conductive materials.
The electrode configuration of such a capacitive MEMS device allows for closed-loop operation in which the device is held fixed in place by electrostatic forces or for differential sensing of an open-loop measurement of the device. Many encapsulation methods used to produce capacitive MEMS devices, however, either do not allow for an arbitrary placement of one or both of the upper and lower electrodes or do not allow for any such out-of-plane electrodes.